It does not have a capacitor squeal normally - it's very quiet, I can't even hear it over my case fans. It only did the squealing / rumbling sound when I used a 400-Watt PSU
There is however a capacitor whine like sound when I run something demanding like Prime 95 - only sometimes - and that started happening after my first 750 Watt PSU died in that machine. I can't figure out if it comes from the GPU, as it's somewhere in that area and toward the CPU under the heatsink, and I hope nothing was damaged when my PSU died. Maybe I just didn't notice before as it only happens at certain heavy loads - not in games, but some combination of prime95 and cannot recall what else I had open.

Ok, the answer for that sound is stupidly obvious - it's just my CPU cooler fan starting to make an odd tonal sound JUST around 53% rotation speed, neither below, nor much above. So no bad capacitors, phew! But yes, my GPU does make a disturbing rumbling fan sound if I manually turn its fans up to like 60%, for which there is never any practical need. I suspect it was a probable reason my GTX 580 was returned back to NewEgg and then resold as open box - someone was probably trying to overclock it and cranked up its fans and was unpleasantly surprised For me though, it stays super quiet at low temperatures without a significant overclock.